1. Field of the Invention
The present invention relates to a transient voltage detection circuit, especially to a transient voltage detection circuit in an electronic system capable of triggering a resetting device of the electronic system.
2. Description of the Prior Art
If a protection device is not installed in a common electronic system, while the electronic system is operating, the voltage thereof will be unstable due to external interference or the electromagnetic effect of the elements in the circuit board; thus, each element in the circuit will be forced to function under the environment of an unstable voltage, possibly causing an error in the system, a systemic crash, or even damage of elements. To solve the above problem, the prior art installs a manual reset device in the circuit, e.g. an electric switch with a button, so that a user, according to his/her experience, may judge whether the reset device should be driven to reset the electronic system.
An automatic reset circuit with the function of detecting transient voltage variation is disclosed in U.S. Pat. No. 5,999,392. The automatic reset circuit is used for detecting the transient voltage variation between the power supply and the ground, so as to reset the electronic system immediately. According to the invention, when a transient interference or disturbance occurs between the power supply and the ground in the circuit, the system can be reset immediately to avoid abnormal functioning of the elements in the circuit.
The detecting unit revealed in U.S. Pat. No. 5,999,392 detects the transient voltage variation by the manner of voltage-couple, and it occupies a larger area, so it is not suitable for small electronic apparatus, e.g. personal digital assistant (PDA), mobile phone, and so on. Moreover, while a transient voltage variation occurs between the power supply and the ground, damping will occur in the voltage of the power supply or the ground with time and space. Because the detecting unit itself also needs appropriate power to maintain normal operation, when a transient voltage variation occurs between the power supply and the ground, damping will also occur in the voltage of the power supply or the ground connecting to the above detecting unit. At this moment, the state of the detecting unit is difficult to be predicted, and it is difficult to predict whether the detecting unit can operate accurately in accordance with the design of which the voltage is under normal condition. In other words, when a transient voltage variation occurs between the power supply and the ground, it cannot be confirmed whether the detecting unit will work as if the voltage is normal. Thus, it is difficult for the above automatic reset device with the function of detecting transient voltage variation to achieve the expected function. In other words, although there is a transient voltage variation, the detecting unit may not detect it and maintains the original state. The behavior of the detecting unit is related to the position thereof and the manner of power damping, so the effect of power damping will be different if the detecting unit is located at different positions of the circuit. Therefore, the detection function of the detecting unit of the prior art is limited.
Therefore, the objective of the present invention is to provide a transient voltage detection circuit to solve the above problem.